<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    let arr = [
        {id: 1, name: '部门1', pid: 0},
        {id: 2, name: '部门2', pid: 1},
        {id: 3, name: '部门3', pid: 1},
        {id: 4, name: '部门4', pid: 3},
        {id: 5, name: '部门5', pid: 4},
    ]

    let result = [
        {
            id: 1,
            name: '部门1',
            pid: 0,
            children: [
                {
                    id: 2, name: '部门2', pid: 1
                },
                {
                    id: 3, name: '部门3', pid: 1,
                    children: [
                        {
                            id: 4, name: '部门4', pid: 3,
                            children: [{id: 5, name: '部门5', pid: 4}]
                        }
                    ]
                },
            ]
        },
    ]

    for (let i = 0; i < arr.length; i++) {
        for (let j = i + 1; j < arr.length; j++) {
            if (arr[i].id === arr[j].pid) {
                if (Array.isArray(arr[i].children)) {
                    arr[i].children.push(arr[j])
                } else {
                    arr[i].children = []
                    arr[i].children.push(arr[j])
                }
            }
        }
    }

    console.log(arr);
</script>
</body>
</html>
